1. Technical Field
The present invention relates to a screwdriver that sequentially launches and drives screws held through a screw chain belt into a part to be threaded-fastened by delivering the screw chain belt by one pitch as the screw is driven.
2. Description of Related Art
Such type of screwdriver is used to fix a gypsum board to a base material such as wood or steel using screws and has been proposed in the related art (for example, see Japanese Patent No. 2900982 and Japanese Registered Utility Model No. 2,550,301).
A conventional screwdriver will be described below with reference to the accompanying drawings.
FIG. 9 is a side view of a conventional screwdriver, FIG. 10 is an exploded perspective view of a screw-delivering mechanism of the screwdriver, FIG. 11 is an exploded perspective view of a slider of the screwdriver, FIG. 12 is a bottom cross-sectional view of a clutch mechanism of the screwdriver, and FIG. 13 is a partial cross-sectional view illustrating threaded fastening using the screwdriver.
Reference numeral 2 indicates a housing in the screwdriver 1 shown in FIG. 9. The housing 2 accommodates a motor (not shown) as a driving source and an output shaft 3 rotated by the motor (see FIG. 13) therein, and a bit 4 is fitted at the end of the output shaft 3 as shown in FIG. 13. A driver portion consists of the housing 2, the motor and the output shaft 3 accommodated in the housing, and the bit 4 fitted at the end of the output shaft 3.
As shown in FIG. 9, a rectangular barrel-shaped slider case 5 is fixed to the front of the housing 2 and an L-shaped guide slot 6 is formed on one side of the slider case 5. A slider 7 is fitted and slides in the slider case 5, and is pushed in one direction (toward the left side in FIG. 9) during normal conditions by a coil spring 8 compressed between the slider and the slider case 5.
The slider 7, as shown in FIGS. 10 and 11, is formed by assembling left and right parts 7A and 7B and an arc guide slot 7a is formed on the side of the part 7A. A screw-delivering mechanism is mounted in the slider 7, which includes a shaft arm 19, a drum 11, a clutch 20, and a coil spring 10.
The shaft arm 19 has a shaft-like guide arm 19a and a lever 19b perpendicularly fixed to the guide arm 19a. The shaft arm 19 is supported in the slider 7 by inserting a shaft 21 into a hole 19c formed through the lever 19b and is capable of rotating. The guide arm 19a of the shaft arm 19 is inserted into a guide slot 7a formed through the part 7A of the slider 7. An end of the guide arm protrudes from the slider 7 (left part 7A) and is fitted into the guide slot 6 formed through the slider case 5. A U-shaped engaging groove 19d is formed at the end of the lever 19b of the shaft arm 19.
The drum 11 is a cylindrical part that is supported by a shaft and capable of rotating in the slider 7 and two disc-shaped flanges 11b and 11c are fitted into a shaft 11a of the drum 11 at an axially predetermined space. A plurality of teeth to be engaged with a screw chain belt 100 (shown in FIG. 9) is formed on the circumference of each of the flanges 11b and 11c. 
A ratchet 11e is formed on the outside of the flange 11b of the drum 11 and a ring-shaped clutch 20 engaged with the ratchet 11e is supported by the rotating shaft 11a of the drum 11 and capable of rotating. The clutch 20 is pushed toward the drum 11 by the coil spring 10 between the clutch and the slider 7 (left part 11A). As a result, pressed against the ratchet 10e of the flange 11b. A pin 20a protrudes from the outside of the clutch 20 and is engaged with the engaging groove 19d formed at the lever 19b of the shaft arm 19.
Operation of the screwdriver 1 having the above configuration will be described below.
As shown in FIG. 9, in fixing a gypsum board W2 to a base material W1 such as wood or steel by using screws, when the screwdriver 1 is pressed against the gypsum board W2, the slider 7 is pushed into the slider case 5 (downward in FIG. 13) against a reacting force of the coil spring 8 and the shaft arm 19 rotates about the shaft 21. In other words, as the guide arm 19a of the shaft arm 19 supported in the slider 7 slides along the guide slot 6, the lever 19b rotates about the shaft at a predetermined angle. As a result, the clutch 20 also rotates in the same direction at the same angle by the rotation of the lever 19b. As the clutch 20 rotates, the drum 11 rotates due to the ratchet 11e engaged with the clutch 20, and the screw chain belt 100 engaged with both of the flanges 11b and 11c of the drum 11 is intermittently delivered from the slider case to predetermined distance. As a result, the screws 101 held through the screw chain belt 100 are delivered one-by-one.
When the screws 101 are delivered as described above, a screw 101 positioned on an axis of the bit 4 of the driver is launched from the screw chain belt 100 and driven into the gypsum board W2 by the bit 4. The screw 101 fastens the gypsum board W2 to the base material W1, and is driven by the bit 4, which is rotated by a motor (not shown).
As the screwdriver 1 is detached from the gypsum board W2, the slider 7 returns to the initial position and slides in the slider case 5 by the reacting force of the coil spring 8. The clutch 20 reverses as the slider 7 slides, but the reverse rotation is not transmitted to the drum 11. Therefore, the screw chain belt 100 and the screws 101 are not delivered.
By repetition of this operation, the screw chain belt 100 is delivered by one pitch and the screws 101 held by the screw chain belt 100 are sequentially delivered into the slider one-by-one, which allows the gypsum board W2 to be fastened to the base material W1 by several screws 101.